1. Field of the Invention
This invention relates to a florescence endoscope apparatus in which excitation light is radiated to a biological tissue and a lesion in the biological tissue is observed with fluorescent light that emits from the biological tissue.
2. Description of Related Art
In a fluorescence observation with an endoscope, if a living body is dyed with a plurality of fluorescent dyes or if auto-fluorescence of the living body occurs or contents such as stool emit fluorescence, the image of the living body is in a state in which many varieties of fluorescent lights are multiplexed. However, if the image of the living body in which the lights are multiplexed is observed as it is, it becomes hard to find the positions of lesions in which the fluorescent dyes accumulate, such as cancer. Accordingly, it is necessary to separate individual fluorescent lights.
Conventional methods for separating individual fluorescent lights from the multiplexed fluorescence image include a method which is aimed at calculating the densities of the respective fluorescent dyes in an object to be measured and is called Unmixing.
The procedure for separating fluorescent lights in Unmixing will be conceptually explained using FIG. 1. In this case, it is supposed that it is already known that two kinds of known fluorescent dyes (fluorescent substances) 1 and 2 exist in an object to be measured.
First, the fluorescence spectrum of each of the fluorescent dyes 1 and 2 which exist in the object to be measured is measured at a set standard density in advance. In this case, FIG. 1A shows one example of the fluorescence spectrum of the fluorescent dye 1 at the standard density, and FIG. 1B shows one example of the fluorescence spectrum of the fluorescent dye 2 at the standard density.
Next, the fluorescence spectrum of the measured object in which the fluorescent dyes 1 and 2 exist is measured. FIG. 1C shows one example of the fluorescence spectrum of the measured object.
Next, the densities of the fluorescent dyes 1 and 2 are calculated with the measurement data of the fluorescence spectra of the fluorescent dyes 1 and 2 at the standard density which are shown in FIGS. 1A and 1B, in order to obtain the measurement data of the fluorescence spectrum of the measured object which is shown in FIG. 1C. FIG. 1D schematically shows one example of the division of the measurement data of the fluorescence spectrum of the measured object shown in FIG. 1C into the respective fluorescence spectra of the fluorescent dyes 1 and 2 having predetermined densities.
Next, a method of calculating the densities of respective fluorescent dyes in Unmixing will be explained.
The signal intensity Iall(λn) of an object to be measured at a wavelength λn is the sum of the signal intensities of the respective fluorescent dyes at the wavelength λn and is expressed by the following equation (2):Iall(λn)=I1(λn)+I2(λn)+ . . . +Im(λn)  (2).where I1 denotes the signal intensity at the wavelength λn which is obtained from a fluorescent dye 1, I2 denotes the signal intensity at a wavelength λn which is obtained from a fluorescent dye 2, and Im denotes the signal intensity at a wavelength λn which is obtained from a fluorescent dye m.
Now, the signal intensity which is obtained from each of the fluorescent dyes is proportional to the density of each of the fluorescent dyes. Accordingly, in the case where m kinds of fluorescent dyes exist in the object to be measured, the signal intensities at a wavelength λn which are obtained from the respective fluorescent dyes can be expressed by the following equations (3a) to (3c):I1(λn)=a1(λn)*D1  (3a).where D1 denotes the density of the fluorescent dye 1, and a1(λn) denotes the coefficient for the fluorescent dye 1 at the standard density at the wavelength λn.I2(λn)=a2(λn)*D2  (3b).where D2 denotes the density of the fluorescent dye 2, and a2(λn) denotes the coefficient for the fluorescent dye 2 at the standard density at the wavelength λn.Im(λn)=am(λn)*Dm  (3c).where Dm denotes the density of the fluorescent dye m, and am (λn) denotes the coefficient for the fluorescent dye m at the standard density at the wavelength λn.
In the case where it is supposed that m kinds of the fluorescent dyes exist in the object to be measured, the signal intensities of the measured object at n wavelength values λ1 to λn can be expressed, for example, by the following matrix equation (4) with these equations (3a) to (3c):
                              (                                                                                          I                    all                                    ⁡                                      (                                          λ                      ⁢                                                                                          ⁢                      1                                        )                                                                                                                                            I                    all                                    ⁡                                      (                                          λ                      ⁢                                                                                          ⁢                      2                                        )                                                                                                      ⋮                                                                                                          I                    all                                    ⁡                                      (                                          λ                      ⁢                                                                                          ⁢                      n                                        )                                                                                )                =                              (                                                                                a                    ⁢                                                                                  ⁢                    1                    ⁢                                          (                                              λ                        ⁢                                                                                                  ⁢                        1                                            )                                                                                                            a                    ⁢                                                                                  ⁢                    2                    ⁢                                          (                                              λ                        ⁢                                                                                                  ⁢                        1                                            )                                                                                        …                                                                      am                    ⁡                                          (                                              λ                        ⁢                                                                                                  ⁢                        1                                            )                                                                                                                                        a                    ⁢                                                                                  ⁢                    1                    ⁢                                          (                                              λ                        ⁢                                                                                                  ⁢                        2                                            )                                                                                                            a                    ⁢                                                                                  ⁢                    2                    ⁢                                          (                                              λ                        ⁢                                                                                                  ⁢                        2                                            )                                                                                        …                                                                      am                    ⁡                                          (                                              λ                        ⁢                                                                                                  ⁢                        2                                            )                                                                                                                    ⋮                                                  ⋮                                                  ⋮                                                  ⋮                                                                                                  a                    ⁢                                                                                  ⁢                    1                    ⁢                                          (                                              λ                        ⁢                                                                                                  ⁢                        n                                            )                                                                                                            a                    ⁢                                                                                  ⁢                    2                    ⁢                                          (                                              λ                        ⁢                                                                                                  ⁢                        n                                            )                                                                                        …                                                                      am                    ⁡                                          (                                              λ                        ⁢                                                                                                  ⁢                        n                                            )                                                                                            )                    ⁢                                    (                                                                                          D                      ⁢                                                                                          ⁢                      1                                                                                                                                  D                      ⁢                                                                                          ⁢                      2                                                                                                            ⋮                                                                                        Dn                                                              )                        .                                              (        4        )            In this case, in the left side of the matrix equation (4),
         (                                                      I              all                        ⁡                          (                              λ                ⁢                                                                  ⁢                1                            )                                                                                      I              all                        ⁡                          (                              λ                ⁢                                                                  ⁢                2                            )                                                            ⋮                                                                I              all                        ⁡                          (                              λ                ⁢                                                                  ⁢                n                            )                                            )  denotes the spectrum of the object to be measured.
Also, in the right side of the matrix equation (4),
         (                                        a            ⁢                                                  ⁢            1            ⁢                          (                              λ                ⁢                                                                  ⁢                1                            )                                                            a            ⁢                                                  ⁢            2            ⁢                          (                              λ                ⁢                                                                  ⁢                1                            )                                                …                                      am            ⁡                          (                              λ                ⁢                                                                  ⁢                1                            )                                                                        a            ⁢                                                  ⁢            1            ⁢                          (                              λ                ⁢                                                                  ⁢                2                            )                                                            a            ⁢                                                  ⁢            2            ⁢                          (                              λ                ⁢                                                                  ⁢                2                            )                                                …                                      am            ⁡                          (                              λ                ⁢                                                                  ⁢                2                            )                                                            ⋮                          ⋮                          ⋮                          ⋮                                                  a            ⁢                                                  ⁢            1            ⁢                          (                              λ                ⁢                                                                  ⁢                n                            )                                                            a            ⁢                                                  ⁢            2            ⁢                                                  ⁢                          (                              λ                ⁢                                                                  ⁢                n                            )                                                …                                      am            ⁡                          (                              λ                ⁢                                                                  ⁢                n                            )                                            )  denotes the fluorescent spectra of the respective fluorescent dyes at the standard density.
Accordingly, the densities of the respective fluorescent dyes D1, D2, . . . , and Dm are found by solving the following matrix equation (5):
                              (                                                                      D                  ⁢                                                                          ⁢                  1                                                                                                      D                  ⁢                                                                          ⁢                  2                                                                                    ⋮                                                                    Dn                                              )                =                                            (                                                                                          a                      ⁢                                                                                          ⁢                      1                      ⁢                                              (                                                  λ                          ⁢                                                                                                          ⁢                          1                                                )                                                                                                                        a                      ⁢                                                                                          ⁢                      2                      ⁢                                              (                                                  λ                          ⁢                                                                                                          ⁢                          1                                                )                                                                                                  …                                                                              am                      ⁡                                              (                                                  λ                          ⁢                                                                                                          ⁢                          1                                                )                                                                                                                                                        a                      ⁢                                                                                          ⁢                      1                      ⁢                                              (                                                  λ                          ⁢                                                                                                          ⁢                          2                                                )                                                                                                                        a                      ⁢                                                                                          ⁢                      2                      ⁢                                              (                                                  λ                          ⁢                                                                                                          ⁢                          2                                                )                                                                                                  …                                                                              am                      ⁡                                              (                                                  λ                          ⁢                                                                                                          ⁢                          2                                                )                                                                                                                                  ⋮                                                        ⋮                                                        ⋮                                                        ⋮                                                                                                              a                      ⁢                                                                                          ⁢                      1                      ⁢                                              (                                                  λ                          ⁢                                                                                                          ⁢                          n                                                )                                                                                                                        a                      ⁢                                                                                          ⁢                      2                      ⁢                                                                                          ⁢                                              (                                                  λ                          ⁢                                                                                                          ⁢                          n                                                )                                                                                                  …                                                                              am                      ⁡                                              (                                                  λ                          ⁢                                                                                                          ⁢                          n                                                )                                                                                                        )                                      -              1                                ⁢                                    (                                                                                                                  I                        all                                            ⁡                                              (                                                  λ                          ⁢                                                                                                          ⁢                          1                                                )                                                                                                                                                                                I                        all                                            ⁡                                              (                                                  λ                          ⁢                                                                                                          ⁢                          2                                                )                                                                                                                                  ⋮                                                                                                                                      I                        all                                            ⁡                                              (                                                  λ                          ⁢                                                                                                          ⁢                          n                                                )                                                                                                        )                        .                                              (        5        )            
Besides, in the above-described matrix equation, when the number of varieties of the spectral images is equal to that of varieties of the fluorescent dyes (or, n=m), the equations are as many as varieties of the densities of the fluorescent dyes, so that the matrix equation can be uniquely solved. Also, when the number of varieties of the spectral images is larger than that of varieties of the fluorescent dyes (or, n>m), although the number of the equations is larger than that of varieties of the densities of the fluorescent dyes, the matrix equation can be solved with the least squares method or the like, in this case. As compared with this, when the number of varieties of the spectral images is smaller than that of varieties of the fluorescent dyes (or, n<m), the number of the equations is smaller than that of varieties of the densities of the fluorescent dyes, so that the matrix equation cannot be solved.
Accordingly, the method of Unmixing requires the premise that the number of varieties of the spectral images is equal to or larger than that of varieties of the fluorescent dyes (or, n≧m),
As described above, according to the method of Unmixing, it is possible to calculate the density of each of the fluorescent dyes in each of pixels by acquiring the fluorescent spectra of the fluorescent dyes at the standard density in advance, acquiring a plurality of the spectral images, and performing the calculation of the matrix equation (5) in each of the pixels. The relation between n kinds of spectral images acquired in a set pixel and the spectrum in the matrix equation is conceptually shown in FIG. 2.
In FIG. 2, Iall(λ1) denotes the intensity of a spectral image 1 and Iall(λn) denotes the intensity of a spectral image n.
Conventionally, such a method of Unmixing is described, for example, in WO 2005/036143, Japanese Patent Kokai No. 2006-242899, or Japanese Patent Kokai No. 2005-181276.